The present invention relates to a valve assembly for a fluid dispensing gun adapted to dispense one or more fluid components onto or into a substrate.
A prior art dispensing gun shown in U.S. Pat. No. 6,158,624 entitled “Foam Dispensing Gun” and assigned to The Clayton Corporation is operable to dispense two fluid components which are mixed in a nozzle of the gun so that the components react with one another to form a foam. In the embodiment shown in the patent, the gun includes a cup 31 having side-by-side fluid flow passages and a valve assembly to control the flow of fluid components through the passage. Each flow passage includes an upstream bore 51 and a downstream bore 53 of smaller diameter. (See FIGS. 2A and 2B of U.S. Pat. No. 6,158,624). The valve assembly comprises a pair of needles 81, each having a forward end received in the downstream bore 53 of each passage. O-rings 85 mounted on rearward ends of the needles seat against shoulders of the cup at the forward ends of the bores 51, thereby sealing the passages against the flow of respective fluid components. Depressing the trigger 141 causes movement of the cup 31 and the shoulders thereon relative to the respective O-rings to allow the components to flow through the flow passages and to be dispensed from the gun.
While the patented design is an improvement over prior designs, control over the flow rate of each fluid component is limited. A relatively small movement of the trigger fully opens the valve assembly so that the fluid components flow through their respective passages at the maximum flow rate. Thus, the flow rate of the fluid components is not easily controlled, especially at low flow rates. Ideally, the flow rate of the fluid components should be controllable through substantially the full range of trigger movement.
The two O-ring seals are often not identically shaped due to manufacturing imperfections or due to deformation or warping that occurs during use of the gun. In a dual component system such as U.S. Pat. No. 6,158,624, if the seals are not identically shaped, then as the valve assembly is opened more of one fluid component may flow past one seal than the other. Thus, the desired ratio of the two components is not maintained.